Electric control apparatus



Aug. 30, 1955 R. J. EHRET 2,716,686

ELECTRIC CONTROL APPARATUS Original Filed May 5, 1950 FlG.l 7

, a; NW NW IIIIIIHHIIIIIIHH HIIIIIIIIIIIIIIIIII ,HHIHHHHHHH INVENTOR.ROBERT J EHRET M4WM ATTORNEY.

2,716,686 Patented Aug. 30, 1955 ELECTRIC CoNrRoL APPARATUS Robert J.Ehret, Philadelphia, Pa., assigrior to Minneapolis-Honeyweil RegulatorCompany, Minneapolis,

Minn., a corporation of Delaware Original application May 5, 50, SerialNo. 160,158, now Patent No. 2,694,169, dated November 9. 1954.

Divided and this application November 23, 1953, Se

rial No. 393,680

3 Claims. Cl. 201-63) The present invention relates to a control deviceof the thermal type, and particularly to a thermal unit includingthermally related electrical heating means and temperature responsiveresistors, and having utility in controlling automatic reset actions inelectric control apparatus of the thermal bridge type.

This invention is a division of my prior application, Serial No.160,158, filed on May 5, 1950, now Patent No. 2,694,169 of November 9,1954. Said patent discloses and claims improved measuring andcontrolling apparatus for electrically effecting proportional controlwith automatic reset action, consisting of a novel and effectivecombination of electrical means for automatically or manually effectingproportional control of a variable quantity such as temperature, withelectrical means for electrically modifying the proportional controlaction by reset action. The modified control action thus produced isdependent upon the direction and magnitude of the departure of thecontrolled variable from a normal or set-point value of the latter, andupon the duration of the period during which the departure hascontinued.

The present invention was primarily devised for use in a reset device sothat the reset action is produced and regulated by heating action ofregulated heating currents passed through heating elements thermallyassociated with temperature responsive resistors which decrease inresistance in a predetermined manner as their temperatures areincreased.

Thus, an object of the present invention is to provide a novelstructural assemblage comprising two temperature responsive resistorsand a heating element arranged in such manner that one resistor willheat up more rapidly than the other even though the two temperatureresponsive resistors are so formed as to have similar resistances whenat the same temperature, and are so arranged that in each prolongedreset action, both resistors will ultimately attain the same maximumtemperature.

In a preferred embodiment of the invention, this novel structuralassemblage for producing a desired reset action comprises a pair ofsimilar temperature responsive resistors, a metallic container enclosingsaid resistors, heat insulation material thermally isolating one of saidresistors from said container and from the other resistor, and electricheating means for heating said container and thereby said resistors atdissimilar rates, said electrical heating means comprising a heatingwire wound about said container.

The various features of novelty which characterize my invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,however, its advantages, and specific objects attained with its use,reference should be had to the accompanying drawings and descriptivematter in which I have illustrated and described a preferred embodimentof the invention.

Of the drawings:

Fig. l is an enlarged side elevation of a thermal unit according to thepresent invention comprising two temperature responsive resistors and aheating resistor;

Fig. 2 is an end elevation of the unit shown in Fig. 1; and

Fig. 3 is a section on the line 3-3 of Fig. 2.

The thermal unit shown in Figs. 1, 2, and 3 comprises a copper rod 66 toone side of which a first or slow temperature responsive resistor 10 issoldered. A sheet of 1 glass wool or analogous heat and electricalinsulation discs or heads 69 and 70,

I end of the resistor material 67 is spirally wound about the rod. Thecopper rod 66, with the insulating layer 67 wound about it, is insertedin a cylindrical copper receptacle or can 68. The ends of the cylinder68 are closed by copper end soldered to the ends of the cylinder. Asecond or fast temperature responsive resister 8 is soldered to theinner side of the end disc 69. A mass of glass wool 71 or analogousinsulating mterial is interposed between the disc 69 and the adjacentend or the rod 66 and insulation material 67 wound about the rod 66. Asimilar insulation mass 72 is interposed between the disc 70 and theadjacent ends of the rod 66 and insulation layer 67.

A terminal conductor 73, soldered to the inner side of the fast resistor8, and electrically insulated from the can 68, passes along the innerside of the latter to and through the insulation mass 72 and then out ofthe can 68 through its end wall 70. The second terminal of the fastelement 8 is formed by the metallic can 68. A terminal 74, soldered tothe can 68 and also to the end of the rod 66, extends longitudinally ofthe thermal unit between adjacent inner and outer convolutions of theinsulation material 67 into and through the insulating mass of material72. A terminal 75, soldered to the 10 remote from the rod 66, similarlypasses to and between adjacent convolutions of the insulating material67 and the insulation mass 72 through the disc 70. As shown, theportions of the terminals 73 and 75 passing through the insulatingmaterial 72 in proximity to the copper rod 66 and then passing throughthe disc 70 are surrounded by electrical insulation tubes 73 and 75,respectively.

The outer cylindrical wall of the receptacle 68 is surrounded byelectrical insulation material 76 on which a heating resistor in iswound with its terminals 48 and 53 extending away from the unit. Theheating resistor m may consist of fine wire, and may have a resistanceof 17,000 ohms. The resistance of the individual resistor elements 8 and10, when at a temperature of F., may well be of the order of 30,000 to50,000 ohms, and may diminish to an operative minimum of the order of1000 ohms when heated to a temperature of 265 F.

A practically important feature of the invention is the enclosure of thefast and slow resistors 8 and 10 in a single can in the mannerillustrated in Figs. 1, 2, and 3, so that the only significanttemperature difference between the two temperature responsive resistorsin the can is that due to the greater thermal inertia of the slowresistor as a result of the relatively low heat transfer coefiicientbetween the heating resistor and slow resistor in the can and the heatstorage capacity of the copper rod 66 in the can. The inclusion ofassociated fast and slow temperature sensitive resistors 8 and 10 alongwith the associated heating resistor in in the same metallic can or unitreceptacle is of much practical importance and contributes directly andmaterially to the excellent overall performance and operative resultsobtained with the measuring and control apparatus of my aforementionedpatent. With the resistors of the unit enclosed in the same can ormetallic receptacle, the unit is made immune to thermal gradients whichhave been found to be practically objectionable in apparatus heretoforeproposed including fast and slow resistors for use in obtaining resetaction.

While, in accordance with the provisions of the statutes, 1? have.illustrated and, described a preferred embodiment of. the presentinvention, those skilled in the art will understand that. changes may bemade in the form of. the apparatus disclosed without departing from thespirit of my invention as set forth in the appended claims, and thatsome features of the present invention may sometimes be used withadvantage, without a corresponding-use of other features.

Having now described my invention, what I claim. as new and desireto'secure byv Letters Patent, is:

l. A reset delay unit comprising a pair of similar resistors, a metalliccontainer enclosing said resistors, heat insulating material isolatingone of said resistors from said container and from the other resistor,and electrical heating means for heating said container and therebyheating said resistors at dissimilar rates.

2. A reset delay unit comprising a pair of resistors, a metalliccontainer enclosing said resistors, heat insulation material thermallyisolating one of said resistors from said container and from the otherresistor, and electrical heating means comprising a wire wound aboutsaid container.

3. A reset delay unit comprising a pair of similar resistors, a mass ofheat conducting metal associated and in good heat transfer relation withone of said resistors, electrical heating means for heating saidresistors, and heat insulation material isolating said mass and theassociated resistor in good heat transfer relation therewith from theother resistor, whereby the latter will heat up more rapidly than theresistor associated with said mass.

No references cited.

